In a storage system, a storage controller performs control of IO with respect to a storage device that is a final storage apparatus for data. Along with an increase in the amount of data handled in companies in recent years, costs for data storage is also increasing due to an increase in storage devices necessary for storing data. Therefore, a reduction in cost for holding data in a storage system is desired. As one technique that addresses this need, there is a technique of reducing the data storage amount by compressing data stored in a storage device (e.g., hard disk drive (HDD) or solid state drive (SSD)). Due to the increase in data amounts, it is desired that data compression techniques be applied not only to a volume for backup application but also to a volume (primary volume) used in normal operations.
Regarding the compression technique, PTL 1 discloses a technique in which a flash device implements data compression processing in order to reduce the data volume stored in the flash device such as an SSD in which a recording medium is a flash memory with high bit cost.